Department of Primatology

Current Project

Foraging Cognition

Primates, and especially humans, have a relatively large body and brain size that are in continuous need of energy, making food acquisition a significant factor for natural selection on their cognition. In order to find highly valued food a primate needs spatial knowledge (where to go?), temporal knowledge (when to go?), ecological knowledge (what are the reproductive strategies of plants, their nutritional contents, past weather conditions and consumption rates of other foragers?) and social knowledge (where do others want to go and what do they know?). My studies attempt to investigate all four components of foraging cognition in humans, apes and monkeys in similar environmental contexts, such as a tropical rain forest environment. To do so, I integrate knowledge from and research methods used in the fields of ecology, psychology, anthropology, and evolutionary biology .The results are expected to produce novel insights in to human cognitive evolution.

Studying Foraging Cognition in the Wild

In cognitive science, there is a growing consensus that especially sensory changes produced by motor actions are critical for both the development and maintenance of cognitive capacities. Animals that are never exposed to a large variety of information and that lack the ability for large-scale movement to integrate environmental cues, such as captive animals, are proposed to show different cognitive performance levels. Hence, to reveal the extent of cognitive performances in primate species it is essential to also study wild primates and human foragers who still collect their own food on a daily basis.

Novel field methodology

Field researchers (and their study subjects) face many conditions that can easily interfere with variables of interest - those that are, some say, “impossible” to control for. Hence, I developed a novel observational field methodology initially necessitated by the difficulties of conducting experiments with highly endangered species, such as chimpanzees. This methodology entails a series of steps. For matters of space I describe the first and the last. In the first step, I study the ecology of primates and their food sources to make predictions on the context in which they would use particular cognitive strategies. By applying such detailed ecological knowledge I was the first to show future planning in a foraging context in wild primates as well as an ability for them to use intuitive statistics to increase their success of discovering newly emerged fruit. The combination of ecological knowledge on fruit production patterns with a priori sampling designs that included exceptionally long observational records of individual primates (up to 100 days) furthermore enabled me to have complete knowledge on their experience and to be the first to find evidence for the use of year-long or across-seasonal memory when primates monitor new food sources, as well as evidence for the social constraints faced in this exact context. The last step focusses on the a-posteriori design, where well-thought-out statistical models, based on decades of biological knowledge, can help to control for important confounding variables.

How do humans and our closest relatives compare when they forage for food?

To better understand the evolution of human cognition and how humans have evolved a brain that is three times the size of our closest relatives, I initiated a project that compares the foraging behaviour of chimpanzees and humans. To gain insight into the evolutionary origins of human behaviour, primatologists have traditionally compared the cognitive abilities of captive great apes and Westernized Educated Industrialized Rich and Democratic (W.E.I.R.D.) people. My research improves on this approach by comparing chimpanzees and human foragers who have a similar social structure (same group size and fission-fusion lifestyle) and grow up in similar rain forests. To maximize comparability we observed the behaviour of Mbendjele BaYaka women and children, living in the rainforest of the Republic of Congo using the exact same data collection methods as with the chimpanzees. Apart from foraging behaviour we also tracked their travel routes with handheld GPS devices, recorded food density and distribution and nutritional data and kept track of group compositions, social interactions, demography, and musical behaviours (because this group is special for the link they make between music and food acquisition). The publication of these results will enable hypotheses testing of theories on human brain evolution, provide novel insights into the benefits of information transfer and musicality, as well as improve methodological approaches for comparative studies on the navigational abilities of primates and other animals.

My Laboratories

Most of my “laboratories” are in the African tropical rainforest and are subject to fast habitat loss and globalization. Recent estimates revealed that the western chimpanzee has reached the last thread status before extinction. The majority of nomadic African human forest foragers currently live in industrialized logging concessions which governments auction off to international companies. Rapid habitat destruction, bushmeat trade, and shifts in land use will likely make primate and human lifestyles disappear within decades. The primary goal of my future research, therefore, has urgency: to apply my novel method for quantifying the behaviour of human and primate forest foragers to obtain truly comparative data that are needed to test hypotheses about the evolution of primate cognition, before this is no longer possible. We are likely the last generation of researchers who can quantify how human and non-human primates forage for food in tropical rain forests. Second, I aim to improve our understanding of the plasticity of foraging cognition by using my acquired methodological skills to compare cognitive performances in a variety of populations (e.g., wild vs zoo). Third, I aim to improve knowledge on the origins of our own cognition by studying the benefits of cognitive abilities that are unique to humans, such as language and music, as well as the potential physiological mechanisms involved in brain development in human foraging populations.

Chimpanzees

Since 2008 I have been studying the ranging and foraging behaviour of Taï chimpanzees (Pan troglodytes verus), investigating the extent of their botanical knowledge and the cognitive strategies they use to find energy-rich ripe fruit. My studies aim to test for the existence of cognitive capacities that enable mental time travel, such as episodic-like memory and future planning and the contexts in which they are used.

In addition, I investigate how individuals can benefit from the reservoir of botanical knowledge of other community members and their use of social cues to find food. The fission-fusion system of chimpanzees provides a unique opportunity to investigate the costs and benefits of gregariousness in relation to locating food and will increase our understanding of the trade-offs made in human fission-fusion systems.

Observations on five adult chimpanzee females with offspring (<7yrs) were conducted over three consecutive years during the same fruiting seasons and comprise consecutive followings of up to 44 days totalling 275 full days. During these periods we recorded the females’ foraging behaviour, travel routes and food locations from the moment they woke up untill the time they made their sleeping nest. The data are being combined with long-term data (>11yrs.) on feeding and ranging behaviour of our target individuals, the phenology of the fruit trees within their territory and the mapped locations of 15,000 fruit producing tree individuals of the 17 most important species in their core area. My work is conducted in close collaboration with my PhD student Simone Ban from the Université Félix Houphouët Boigny in Côte d’Ivoire.

Mbendjele BaYaka

Since 2015 I started investigating the extent with which humans use episodic memory and flexible planning in the tropical rainforest environment. I, in addition, plan to investigate their species- and plant-specific knowledge of the temporal distribution of their food and how this knowledge corresponds to that of our closest relatives the chimpanzee that lives in similar forests feeding on the same plant food and humans living in different environments where food can be more easily spotted by sight.

The second part of my studies will focus on the questions whether, when and with whom human rainforest foragers share knowledge about food locations, whether information transfer (by language, vocal or gestural reading) increases food finding efficiency and how information of food locations is valued by the community.

To answer these questions we will record the ranging and foraging behaviour of five Mbendjele Yaka women and their families, living in the rainforest of the northwestern Congo basin bordering the Motaba river, for 28 consecutive days each within two consecutive years during the same fruiting seasons. During these periods we plan to record the women’s foraging behaviour, travel routes and food locations from the moment they leave camp till the moment they end their foraging trip. In addition, to our observational work on the women, we will assess the value of alternative foraging choices (through botanical transects) and will conduct a variety of non-invasive food finding experiments. My team exists of me, my Korean PhD student Haneul Jang, a Congolese PhD student Bill Loubelo and one volunteer (Seung lok Paik) and the study is conducted in close collaboration with Prof. Dr. Christophe Boesch. If you see opportunities for comparative analyses or other use of our data, feel free to contact me.

Mangabey monkeys

In this project I investigate whether sooty mangabeys (Cercocebus atys atys) make use of the sounds of other foragers to increase their food finding or foraging efficiency. We test whether the mangabeys use the sounds of nutcracking chimpanzees (Pan troglodytes verus) and red river hogs (Potamochoerus porcus) to locate and scavenge on the remains of cracked nuts. We, in addition, compare the monkeys’ approach behaviour with that of guinea fowls (Agelastes meleagrides; Guttera pucherani) and rodents (Cricetomys spp., Heliosciurus spp.) that also feed on nuts.

We make use of camera traps placed at a variety of locations in the rainforest of the Taï National Park in Côte d’Ivoire. The work is conducted by my Bachelor student Bryndan van Pinxteren and is co-supervised by Dr. Martijn Egas from the Institute of Biodiversity and Ecosystem Dynamics at the University of Amsterdam. The camera trap data is made available to us by PhD candidate Giulia Sirianni and the Pan African Chimpanzee Project led by Prof. Dr. Christophe Boesch and Prof. Dr. Hjalmar Kühl.